The present invention relates to a tape measure and, in particular, to an improved tape measure that allows a user to accurately measure internal dimensions and mark pre-determined distances.
Tape measures are generally used to measure either a distance between two fixed points or a pre-determined distance from a reference point. For example, prior to fitting a door, a tape measure may be used to measure the internal dimensions of the door opening, i.e. the distance between opposed doorjambs. During the fitting of the door, the tape measure may be used to measure a point of installation for a door latch, i.e. a fixed distance from the bottom of the door. It is important that the internal dimensions of the door opening are measured accurately, as otherwise the manufactured door will not fit correctly in the door opening. It is also important that the point of installation for the door latch is measured accurately, as otherwise the door latch will not properly engage the door strike plate when the door is installed.
Unfortunately, there are numerous factors that may affect a user's ability to accurately measure internal dimensions and mark distances with a conventional tape measure. A conventional tape measure is typically only provided with scales graduated to 1/16th of an inch, which is about the finest graduation that can be comfortably distinguished by a human eye. This restricts the accuracy of the measurements to 1/16th of an inch even in applications that may require measurements to 1/32nd or even 1/64th of an inch. It is also difficult to accurately measure internal dimensions with a conventional tape measure. A conventional tape measure housing requires that the measure tape be folded against a corner, thereby preventing a user from obtaining an accurate measurement of the internal dimension. Finally, it is often necessary to measure dimensions and mark distances in dimly lit environments where it is difficult for a user to read the scale.
To overcome the above-mentioned shortcomings, numerous improvements have been made to conventional tape measures. In U.S. Pat. No. 3,205,584 to Over a tape measure is provided with a magnifying lens to allow for more finely graduated scales. In U.S. Pat. No. 6,918,191 to Stauffer et al., a tape measure is provided with mounted rear tail to allow for measurement of internal dimensions. In U.S. Pat. No. 6,030,091 to Li a tape measure is provided with built-in light source to allow for use of the tape measure in dimly lit environments. All of the aforementioned references are incorporated herein by reference.
Although the above-mentioned improvements to conventional tape measures increase the accuracy with which the scale may be read, they do not provide means for accurately measuring dimensions and marking distances. The prior art improvements to conventional tape measures only improve the readability of the scale as a whole. Human error still occurs when a user determines which of the indicia on a scale defines the dimension or distance being measured. This may result in inaccurate measurements being obtained which in turn may lead to improperly fitting materials as discussed earlier. There is therefore a need for an improved tape measure that may be used to accurately measure dimensions and mark distances.